Cancer risk in patients with rheumatoid arthritis treated with janus kinase inhibitors: a nationwide Danish register-based cohort study

Objectives: We aimed to investigate the risk of first primary cancer in patients with RA treated with janus kinase inhibitors (JAKi) compared with those who received biologic DMARDs (bDMARDs) in a real-world setting. Methods: We performed an observational cohort study using the nationwide registers in Denmark. Patients with RA aged 18+ years, without a previous cancer diagnosis, and who initiated treatment with JAKi or bDMARDs from 1 January 2017 to 31 December 2020 were followed for any cancer (except non-melanoma skin cancer). We applied inverse probability of treatment weighting (IPTW) to account for covariate differences between treatment groups. IPTW-generated weights were used with cause-specific Cox (CSC) models to calculate hazard ratios (HRs) for cancer incidence in JAKi-treated compared with bDMARD-treated patients with RA. Results: We identified 875 and 4247 RA patients treated with JAKi and bDMARDs, respectively. The JAKi group contributed 1315 person years (PYRS) and 19 cancers, the bDMARD group contributed 8597 PYRS and 111 cancers, with corresponding crude incidence rates per 1000 PYRS of 14.4 and 12.9. Comparing the two groups using weighted CSC models, a HR of 1.41 (95% CI 0.76, 2.37, 95% CIs) was seen for JAKi- vs bDMARD-treated patients with RA. Conclusion: JAKi treatment in real-world patients with RA was not associated with a statistically significant increased risk of first primary cancer compared with those who received bDMARDs. However, several numerically increased risk estimates were detected, and a clinically important excess risk of cancer among JAKi recipients cannot be dismissed.